BFS Flood Fill algorithm

Project already has Flood Fill

• This project already has a Flood Fill algorithm, but it is DFS.
  For any big "image" DFS version won`t work because of stack overflow.
  The BFS version, on the other hand, handles large "images" without any problems.

• My first "big" project on Java was simple pixel paint app and that was my first time encountering StackOverflowException and I was very confused: it took me some time to figure out the problem and solution.
  So, it would be useful to have this example of this algorithm here.

• A similar version of this algorithm can be found here: https://www.geeksforgeeks.org/dsa/flood-fill-algorithm/
  Main difference - this version looks for diagonals too

Technical details

This version uses queue and helper class Point to traverse.
While queue is not empty, the "pixel" is painted and "pixels" around it are added to queue (if coordinates are in boundaries and colour is not the same).
Directions for new "pixels" stored in arrays dx and dy. First four - horizontal and vertical, second four - diagonals.

It is achievable to store coordinates (x, y) in long, using bit mask, but it`s too much and possibly can lead to collision.

Tests were copied from original FloodFill and one test was added to demonstrate that BFS handles "big images".

To be honest, I am not entirely sure in what package to add this, so "others" was picked.

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java